DESCRIPTION (Verbatim from the applicant's abstract): The long term goal of this laboratory is to identify the required biochemical components and elucidate the molecular mechanisms by which human peroxisomes import their constituent enzymes. Peroxisomes are vital intracellular organelles involved in a vast array of biochemical and metabolic processes. The existence of devastating human genetic disorders in which the peroxisome fails to import its matrix enzymes best illustrates the importance of the organelle in overall human physiology. The vast majority of peroxisomal proteins contain a specific targeting signal, called PTS1, which serves to identify them as import substrates. The basis of this identification is an association with the PTS1-specific receptor molecule, Pex5p. Receptor-substrate complexes then interact with components of the peroxisome membrane, and translocation ensues. Although a number of molecules, called peroxins, have been implicated in various aspects of peroxisome assembly, a detailed description of the fundamental molecular mechanisms associated with peroxisomal protein import is not yet available. Our approach to gaining an understanding of peroxisomal protein import has been to reconstitute various aspects of the process in vitro. In this proposal, we will utilize a number of such assays to examine the intracellular trafficking of Pex5p and PTS1, as well as to gain mechanistic insights into this fundamentally important cellular process. Our multidisciplinary approach will address the following specific aims: 1. To analyze the binding of Pex5p to PTS1. 2. To analyze docking of the Pex5p-PTS1 complex at the peroxisome membrane. 3. To analyze import of Pex5p and PTS1. 4. To analyze Pex5p recycling.